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When processing digital images, particularly color images, it is often necessary to perform a quantizing operation upon the digital values that represent each of the pixels forming the digital image. Color quantization often gives rise to false contouring artifacts in an image formed with these quantized digital values. Contouring occurs when colors of spatially adjacent pixels, that are also close to each other in the color space, Get mapped into different colors by the quantizing process. This contouring is usually highly objectionable because it appears in smooth regions where the human visual system has relatively low tolerance to noise. In particular, the noise is of a correlated nature, taking the form of lines and circles, and hence is easily noticed by the human eye.
The removal of contouring effects in images has been the subject of a number of patents and papers. What the present solution to the problem offers is a quicker way to identify the existence of contours and of applying a correcting algorithm to only those regions of the image that contain the contours.